intraocular lens polymers can be broadly categorized into two groups: (1) materials that absorb less than 1 percent water and (2) materials that absorb more than 1 percent water. Materials that absorb less than one percent water are typically referred to as hydrophobic polymers. Hydrophobic polymers may be foldable at room temperature. Their “foldability” results from their composition rather than from water acting as a plasticizer. Water absorbing polymers are typically referred to as hydrophilic polymers or hydrogels. The most, common materials in this group have approximately 25 percent water by weight. Hydrophilic polymers are usually foldable at room temperature by virtue of absorbed water acting as a plasticizer.
The conventional thinking in the intraocular lens industry is that hydrophilic intraocular lenses must be immersed in water or saline during storage to maintain a level of hydration needed for foldability at room temperature. Accordingly, lenses composed of these materials are almost ways packaged in normal saline (0.9 percent sodium chloride). Such lenses may reside in saline for up to five years prior to implantation. The normal saline in which these lenses are packaged is generally designed to mimic the conditions of the anterior segment of the eye where the lens will reside following implantation. This means that lenses will have similar dimension and mechanical characteristics in the eye as they have in the package where they reside prior to implantation.
Immersion in water or saline in the presence of other plastics needed for retention or insertion of the intraocular lens, however, can result in contamination of the intraocular lens by chemical entities contained in or produced by other plastic components in the packaging system. Being immersed in water or saline, the intraocular lens can “communicate” with plastic components via the liquid phase. Also, when an insertion instrument is removed from the package for use, water can flow from where the instrument was stored within the package to the intraocular lens.
The packaging of intraocular lens in water or saline has the additional disadvantage, especially when the intraocular lens is packaged with an insertion instrument, of increasing the weight of the package, thereby increasing shipping costs.
Moreover, implantation systems for hydrophilic intraocular lenses either require some kind of preparation of the injector or they use concepts of partly preloaded injector designs, e.g. with an adaptable cartridge with the preloaded intraocular lens including some preparation steps. All such preparation steps entail risks associated with possible false preparations or other mishandling by the surgeon or nurse. It is therefore advantageous to reduce the number of required preparation steps to as few as possible. This is especially true with so called MICS intraocular lenses—designed for micro incision cataract surgery. These lenses may require prefolding to facilitate advancement through the tubular region of the injector for better reproducibility of the injection process (with regard to tilting and rotation) and for proper folding of the intraocular lens.